This invention referes to a process for rutile flotation with the use of N-benzoyl-N-phenylhydroxylamine (N-BPHA) as a flotation collector. More particularly, this invention is concerned with a process for the separation of rutile from rutile ores containing iron-bearing components, especially hematite by flotation with N-benzoyl-N-phenyldroxylamine as a flotation collector which forms chelation complex compounds that are stable with titanium but unstable with iron in a well determined concentration and pH range, so that the selective separation of rutile is possible.
The use of chelating agents as flotation collectors has been an experimentation subject for some time, even though with respect to the study of such phenomena per se more than to an analysis of the operating mechanisms. More recently (Peterson et al. 1965, M. C. Fuersstenau et al., 1967, 1970, Marabini and Rinelli, 1975, Nagarau and Somasundaran 1981, etc.) the attention concentrated on the research of flotation collectors of said kind, showing specific selectivity, also as a result of the stimulus of economics motivations.
Difficulties arose in such operation which have not been satisfactorily solved to date, and substantially consisting in the following problems:
(a) the definition of the molecular structure of the chelating agents which should be both water soluble and of sufficient affinity for the air phase in the nonpolar fraction;
(b) the formation of insoluble surface chelates, which is necessary to obtain a suitable selectivity, but with the risk that the excessive chelate stability with respect to the ore crystalline structure may give surface corrosion phenomena, with the possibility of the chelate detachment;
(c) excessive reagent consumption with respect to traditional collectors.
Considering the present situation as depicted above, both as regards the experimentation level and the industrial production and application level, the use is suggested according to this invention of N-benzyl-N-phenylhydroxylamine as a selective collector for rutile ores containing iron-bearing components, especially hematite, which collector allows the reduction or the elimination at a reasonably satisfactory degree of the above mentioned problems.
The fundamental observations which led to the determination of the basic technical teaching suggested in this invention are a result of the study of the rutile/N-benzoyl-N-phenylhydroxylamine system.
As it is well known, N-benzoyl-N-phenylhydroxylamine (N-BPHA) is a hydroxylamine derivative by substitution of two nitrogen atoms with the 1-phenyl and 1-benzoyl groups, according to the following structural formula (I): ##STR1##
N-BPHA can also be considered as an N-phenylbenzoylhydroxamic acid (Perrin, 1979), and the water solubility and the chelating action of hydroxyamic acids are well known. On the contrary, N-BPHA is insoluble in water because of the presence of an aromatic ring which substitutes the hydrogen atom of the oxamic group; however, it is soluble in ethyl alcohol and acetone.
The use is well known of such compound (Kaimal and Shome, 1962) in analytical chemistry for the gravimetric determination of titanium. The chelate compound formed in solution between N-BPHA and titanium, according to the elemental analysis, can be written as follows: ##STR2##
From the analytical experimentation on the use of N-BPHA for titanium determination in the presence of other different cations including Fe.sup.+++ (Kaimal and Shome) the theoretical indication was drawn, according to the preliminary studies for the formulation for this invention, of a higher stability of the N-BPHA complex compound with titanium with respect to that formed with iron, and consequently the indication of a possible activity of N-BPHA as a flotation collector for rutile, with some selectivity for that ore with respect to iron ores such as hematite which are often associated to it in natural products.